Abstract: The influence mechanism of laser scanning speed on the tensile properties of selective laser melting formed 316L stainless steel at 300 K and strain rate of 10¹⁰s^-1was investigated by using molecular dynamics simulations. Through comprehensive stress-strain analysis, common neighbor analysis for crystal structure characterization and dislocation evolution analysis, the atomic-scale mechanism that the scanning speed synergistically enhances strength-ductility through strain-induced BCC phase transformation coupled with grain boundary dislocation pinning effects was revealed. The results show that when the scanning speed decreases to 0.5 Å/ps, the specimen achieves an ultimate tensile strength of 14.487 GPa with 22.9% strain, while the occurrence time of the stress peak is relatively delayed. During deformation, significant strain-induced phase transformation is observed, dynamic transitions among face-centered cubic（FCC）, body-centered cubic（BCC） and hexagonal close-packed（HCP） crystal structures are observed. The BCC and disordered（Other） structures reach their maximum concentrations at the stress peak, and partial reverse transformation during crack propagation stage occurs. The dislocation analysis demonstrates that Shockley partial dislocations dominate the plastic deformation process. Specimens formed at lower scanning speeds（0.5 Å/ps） exhibit more pronounced grain boundary strengthening effect, with their dislocation network evolution showing strong correlation with crystal structure transformations. The work demonstrates that optimizing scanning speed can effectively control the microstructure evolution pathway in SLMformed 316L stainless steel, providing theoretical guidance for enhancing the tensile properties of additively manufactured metallic materials.